1. Field of the Invention
The present invention relates to a development roller. In particular, the invention is directed to a development roller including carbon nanotubes for an electrophotographic device capable of maintaining sharpness of an image while keeping a low resistance and the development roller elastic.
2. Description of the Related Art
Examples of the electrophotographic device include a copy machine, a printer, a facsimile, a composite apparatus, and so forth.
FIG. 1 shows a laser printer among those examples, FIG. 2A shows a development roller of the laser printer shown in FIG. 1, and FIG. 2B is a cross-sectional view of FIG. 2A. The same elements in the same figures refer to the same reference numerals.
An operation principle of the laser printer will be described with reference to FIG. 1.
Toners stored in a toner storage are uniformly and electrically agitated by an agitator. Mechanical and electrical powers of a supply roller 300 attach the agitated toners to a surface of the development roller 200 having a predetermined surface voltage. A blade installed above the development roller 200 then spreads the toners attached on the surface of the development roller 200 to a uniform thickness.
An electrifying roller equally electrifies a surface of a photo-sensitive drum 400 with a high pressure while rotating with the photo-sensitive drum 400. A Laser Scanner Unit (LSU) irradiates a laser beam on the surface of the electrified photo-sensitive drum 400 with a constant voltage to form an electrostatic latent image. The thin layer of the toner uniformly attached on the surface of the development roller 200 are attached to a position where the electrostatic latent image is formed so that a toner image is formed. The toner image is then transferred to a recording medium by a transfer roller.
Referring to FIG. 2A, the development roller 200 is composed of an elastic roller body 210 and a central shaft 220 formed of metal and inserted into the roller body. A high voltage is applied via the shaft 220 so that a surface electric potential is generated on the surface of the roller body 210.
The development roller is classified as a polymer roller and a metal roller according to its primary material. The polymer roller may be classified further as an ion conductive type and an electron conductive type. The ion conductive type is fabricated by adding a salt, generally, an alkoxide salt. The ion conductive type development roller is universal because of its advantageous cost. However, This type has the disadvantage of a high drift in resistance of the roller in response to low temperature and low wet circumstance and high temperature and high wet circumstance. This type also has difficulty in implementing low resistance, and has image defects due to movements of molecules which have not been cross-linked onto the surface of the roller.
The electron conductive type is fabricated by adding a carbon black to the elastic roller body. However, when the excessive carbon black is added so as to implement the desired low resistance, a hardness of the roller body increases to add extra weight to a toner stress, which in turn rapidly degrades the toner durability to weaken the roller durability, so that a life time of the development roller is shortened. In addition, dispersibility of the carbon black is degraded to cause the resistance value to lack uniformity. In addition, the carbon black as fine particles flows out of the roller body to contaminate the inside of the electrophotographic device and the images.